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1.
Smith, J. R. 1987. Potassium transport across the membranesof Chara. II. 42K fluxes and the electrical current as a functionof membrane voltage.—J. exp. Bot. 38: 752–777. The current required to clamp the trans-membrane voltage ofinternodal cells of Chara australis at different levels wasmeasured simultaneously with either the 42K influx or efflux.Examination of the voltage-dependence of the ratio of the electricalcurrent to the unidirectional tracer fluxes yielded no evidenceof any amplification of the electrical driving force on theK+ ions. There was thus no evidence for the interaction of K+ions with themselves or any other species during their passageacross the membrane. These measurements allow the determinationof , the fraction of the electrical current carried by K+ ions.When the external [K+] = 10 mol m–3, the average valueof was 0?85 for Vm > –125 mV and 07?5 for Vm <–150 mV. When the external [K+] = 0?1 mol m–3, was 0?6 for Vm < –80 mV and 0?1 for Vm > –250mV. It was also found that the conductance associated with K+transport was inhibited by hyperpolarization. Key words: Potassium, conductance, flux-ratio  相似文献   

2.
Dunlop, J., Knighton, M. V. and White, D. W. R. 1988. Ion transportand the effects of acetic acid in white clover. I. Phosphateabsorption.—J. exp. Bot. 39: 79–88. The effect of acetic acid on phosphate absorption by white clovertissue has been examined. At 1·0 mol m3 acetic acid phosphateabsorption by roots of intact plants was stimulated by 36% (P< 0.001). At 5.0 and 10 mol m–3 acetic acid there wasmarked inhibition of absorption by both suspension culturesof cells and the roots of intact plants. The inhibition waspH dependent with decreasing pH causing increased inhibition.Acetic acid caused changes in the membrane electropotential(E) with concentrations of 2·0 mol m–3 or lesscausing persistent polarization whereas at 5·0 mol m–3and higher concentrations the polarization was followed by agreater depolarization. Intracellular pH as measured by thefluorescence of fluorescein was lowered by acetic acid. Calculationsindicate that for white clover roots the proton motive force(pmf) appears to provide sufficient energy for phosphate absorption.It is proposed that acetic acid influences phosphate absorptionthrough its dependence on proton cotransport and that changesin J E affect the rate of phosphate absorption because of thedependence of the pmf on E. Key words: Phosphate absorption, intracellular pH, acetic acid, proton motive force, Trifolium repens, membrane electropotential  相似文献   

3.
This work aimed to study the impacts of acquisition and assimilationof various nitrogen sources, i.e. NO3, NH4+ or NH4NO3,in combination with gaseous NH3 on plant growth and acid-basebalance in higher plants. Plants of C3 Triticum aestivum L.and C4 Zea mays L. grown with shoots in ambient air in hydroponicculture solutions with 2 mol m–3 of nitrogen source asNO3, NH4+ or NH4NO3 for 21 d and 18 d, respectively,had their shoots exposed either to 320 µg m–3 NH3or to ambient air for 7 d. Variations in plant growth (leaves,stubble and roots), and OH and H+ extrusions as wellas the relative increases in nitrogen, carbon and carboxylatewere determined. These data were computed as H+/N, H+/C, (C-A)/N,and (C-A)/C to analyse influences of different nitrogen sourceson acid-base balance in C3 Triticum aestivum and C4 Zea maysplants. Root growth in dry weight gain was significantly reduced bytreatment with 320 µg m–3 NH3 in Triticum aestivumand Zea mays growing with different N-forms, whereas leaf growthwas not significantly affected by NH3. In comparison with C3Triticum aestivum, non-fumigated C4 Zea mays had low ratiosof OH/N in NO3–3-grown plants and of H+/N in NH4+- and NH 4NO3-grown plants. Utilization of NH3 from the atmospherereduced both the OHN ratios in NO3 -grown plantsand the H+/N ratio in NH4+ - and NH4NO3 -grown plants of bothspecies. Furthermore, Zea mays had higher ratios of (C-A)/Nin NH4+ - and NH4NO3-grown plants than Triticum aestivum. Thismeans that C4 Zea mays had synthesized more organic anion perunit increase in organic N than C3 Triticum aestivum plants.Within both species, different nitrogen sources altered theratios of (C-A)/N in the order: NH4NO3>NH4+>NO3.Fumigation with NH3 increased organic acid synthesis in NO3- and NH4+ - grown plants of Triticum aestivum, whereas it decreasedorganic acid synthesis in Zea mays plants under the same conditions.Furthermore, these differences in acid-base regulation betweenC3 Triticum aestivum and C4 Zea mays plants growing with differentnitrogen sources are discussed. Key words: Acid-base balance, ammonia, ammonium, nitrate, ammonium nitrate, C3 Triticum aestivum L., C4 Zea mays L.  相似文献   

4.
The euryhaline charophyte Lamprothamnium papulosum (Wallr.)J. Gr. was adapted to media with decreasing salinities rangingfrom 550 to 0 mosmol kg–1. Vegetative plants grown inmedia with osmotic pressures (0) in the range of 550 to 130mosmol kg–1 maintained a constant turgor pressure () at309 + 7 mosmol kg–1. The ions K+, Na+ and Cl–, werethe predominant solutes in the vacuole. Changes in their concentrationsaccount for the variation in internal osmotic pressure (1) with,0. The divalent ions Mg2+, Ca2+ and were also present in significant amounts, but their concentrationsdid not alter with changes in, 0. In cells subjected to hypo-osmotic shock the regulation of was incomplete. The turgor pressure increased from 302 to 383mosmol kg–1. The first rapid response to the sudden decreasein 0 was a loss of K+ and Cl. In contrast to the decreasein ionic concentrations an accumulation of sucrose occurredwhich could account for the increase of . The increase in sucroseconcentration started 24 to 48 h after the downshock and reachedits highest value after 3 to 4 weeks. The sucrose concentrationin the vacuole was up to 320 mol m–3. During this timethe ionic content continued to decrease but did not counterbalancethe sucrose concentration sufficiently to regain the original. High sucrose levels accompanied by an enhanced were also observedduring the period of fructification (sexual reproduction: formationof antheridia and oogonia) in Lamprothamnium kept under conditionsof constant salinity. It is concluded that high sucrose content and elevated arecharacteristic of sexual reproduction in this charophyte. Lamprothamniumis able to tolerate different during various developmentalstages (e.g. vegetative and reproductive phases). Key words: Lamprothamnium papulosum, sucrose, turgor pressure  相似文献   

5.
The uptake of abscisic acid (ABA) by suspension-cultured Phaseoluscoccineus L. cv. ‘Prizewinner’ (runner bean) cellshas been studied. In addition to non-mediated diffusive uptakeof ABAH, a saturable component of uptake occurs which is demonstrableas inhibition of uptake of submicromolar concentrations of [2-14C]ABAby increasing concentrations of nonradioactive ABA to a constantplateau level. Saturation is not due to competition for extracellularbinding sites or cytoplasmic acidification and can only be partiallyaccounted for by saturation of metabolic enzymes. It is consideredlargely to represent carrier-mediated ABA uptake. The maximumvelocity of the carrier is greater at pH 4.0 than at pH 5.0,although the apparent Michaelis constants are similar (about2.0 mmol m–3). No carrier activity was detectable abovepH 6.0. The carrier is unaffected by indol-3-yl acetic acid(IAA), gibberellin A3, benzyladenine or 2, 3, 5-triiodobenzoicacid (TIBA). Use of protein-modifying reagents suggested a roleof histidine residues in carrier activity. Reagents expectedto modify the transmembrane pH ( pH) and electrical ( E) gradientswere used to study the driving forces for ABA uptake. Therewas no apparent effect of E, indirectly monitored by effectson an electrogenic TIBA-sensitive component of IAA transport,on ABA uptake. Both diffusive and saturable components weremodified in proportion by changes in pH, suggesting a commonsensitivity to this driving force. The carrier is suggestedto act as an ABA/H+ symport. Key words: Abscisic acid, Phaseolus coccineus L., Transport, Suspension culture  相似文献   

6.
In Trifolium repens L. there were immediate transient depolarizationsof the membrane electropotential (Evo) when KH2PO4 was addedto phosphate-free media, but these were of the same magnitudeas the controls (K2SO4 and KCI). Furthermore, the extents ofdepolarization were the same as the expected effect of the addedK+ calculated using the Goldman equation. There was no significantdepolarization on adding H3PO4 to buffered media. Consequently,there was no evidence for a depolarization caused by phosphate.This result provides evidence that the H+–H2PO4 symportin roots of T. repens operates with a stoichiometry of 1: 1. In a group of control plants ( + P plants) and a group whichwere stressed by reducing the supply of phosphate (– Pplants), the – P plants had lower values for Evo than+P plants (– 118 mV and – 130 mV, respectively).The absence of phosphate from the measurement media also reducedEvo (mean effect = 9 mV). A significant difference in Evo between– P and + P plants persisted when phosphate was addedto – P plants. The electropotential difference acrossthe tonoplast (Evo) in – P plants became more positivewith time. Key words: White clover, membrane transport, roots, tonoplast, symport  相似文献   

7.
The vacuolar pH (pHv) and the cytoplasmic pH (pHc) of the marinegiant-celled green alga Chaetomorpha darwinii were measuredby pH microelectrode techniques on extracted vacuolar sap, andby the [I4C]DMO distribution method respectively. Equilibrationof DMO occurred with a half-time of about 2 h, with an apparentPDMO of 3.6 x 10–5 cm s–1, but the vacuolar concentrationof free, undissociated DMO was always less than the externalconcentration. The explanation offered for freshwater giant-celledalgae of net DMO leakage across the plasmalemma cannotapply to Chaetomorpha darwinii, since electrically-driven DMOexit from the cytoplasm should be similar across the plasmalemmaand the tonoplast in these cells with large, vacuole-positivepotential differences across the tonoplast. pHc was accordinglycomputed assuming either tonoplast or plasmalemma equilibrationof DMO, with correction for DMO metabolism within the cell.pHc was 8.0–8.3 in the light in artificial seawater (pHoabout 8.0), was some 0.5 units lower in the dark, and was slightlylower with an external pH of 7. Vacuolar pH was 6.5–6.9,without consistent effects of illumination or of external pHof 7 rather than 8. While µH+ at the tonoplast was similarto that in giant-celled freshwater algae (although with a greatercontribution from relative to pH), µH+ at the plasmalemmawas less than 8 kJ mol–1, i.e. less than one-third ofthe value in freshwater green algae. µNa+ was some 13kJ mol–1 at the plasmalemma. The possibility that theprimary active transport process at the plasmalemma of Chaetomorphadarwinii (and certain other marine algae) is Na+ efflux ratherthan H+ efflux is discussed.  相似文献   

8.
Control of Passive Permeability in the Chara Plasmalemma   总被引:2,自引:0,他引:2  
Conductance to K+ alters as a function of membrane potential(m). Conductance to H+ (or OH) changes with externalpH (pHo) This conductance change can be modulated by alteringcytoplasmic pH or external K+ concentration, both of which alsoalter m. We suggest a role for H+ conductance in regulatingcytoplasmic pH above pHo 7.0.  相似文献   

9.
Changes in the concentrations of K+ and Cl occur in parallelduring turgor regulation, and account for the changes in osmoticpressure. Thus it is impossible to single out one ion whoseconcentration is directly controlled by a turgor regulatorymechanism. After an increase in external osmolality (o) of 400mosmol kg–1, turgor is restored to its normal value in4–5 d. The response to a decrease in o is much more rapid,with most of the change in 1 occurring in the first 2 h. Apparentcytoplasmic concentrations of sucrose are similar to vacuolarconcentrations, and increase slightly with increasing 1.  相似文献   

10.
Using the compartmental analysis the unidirectional Na+ fluxesin cortical cells of barley roots, the cytoplasmic and vacuolarNa+ contents Qc and Qv, and the trans-root Na+ transport R'have been studied as a function of the external Na+ concentration.Using the re-elution technique the effect of low K+ concentrationson the plasmalemma efflux co of Na+ (K+-Na+ exchange) and onR' was investigated at different Na+ concentrations and correspondinglydifferent values of the cytoplasmic sodium content Qc. The relationof the K+-dependent Na+ efflux coK+-dep to Qc or to the cytoplasmicNa+ concentration obeyed Michaelis-Menten kinetics. This isconsistent with a linkage of co, K+-dep to K+ influx by a K+-Na+exchange system. The apparent Km corresponded to a cytoplasmicNa+ concentration of 28 mM at 0·2 mM K+ and about 0·2mM Na+ in the external solution. 0·2 mM K+ stimulatedthe plasma-lemma efflux of Na+ and inhibited Na+ transport selectivelyeven in the presence of 10 mM Na+ in the external medium showingthe high efficiency of the K+-Na+ exchange system. However,co, K+-dep was inhibited at 10 mM Na1 compared to lower Na1concentrations suggesting some competition of Na1 with K1 atthe external site of the exchange system. The effect of theNa+ concentration on Na1 influx oc is discussed with respectto kinetic models of uuptake.  相似文献   

11.
Fidgeon, C. and Wilson, G. 1987. Growth regulation of Galiummollugo L. cell suspensions by -naphthalene acetic acid.—J.exp. Bot. 38: 1491–1500. Galium mollugo cell suspension cultures were found to requirethe plant growth regulator -naphthalene acetic acid (-NAA) forcontinued growth and cell division. This requirement could notbe substituted in either batch or semi-continuous culture byindole-3-acetic acid (IAA) or 2,4-dichlorophenoxy acetic acid(2,4-D) at any concentration tested. However, ß-naphthaleneacetic acid (ß-NAA) and indole-3-butyric acid (IBA)were found to support growth when supplied at a concentrationtwo orders of magnitude greater than the normal media level(0–5 mg dm3). The growth of Galium cells was found to be influenced not onlyby the -NAA initially supplied in the medium but also by theexposure to -NAA in previous growth cycles. Preculture of cellsfor 3 d in an -NAA containing medium, followed by cell washingand re-inoculation into -NAA free medium, supported a quantitativegrowth response similar to that obtained after 14 d in the control-NAA containing medium. Even short-term exposures between 0·5and 6·0 h stimulated a detectable growth response 14d later. These observations raise questions relating to theuptake and perception of exogenously supplied growth regulatorsby cultured cells. The delayed kinetics of this form of response is of significancein culture regimes in which cells are transferred from one mediumto another, differing in their growth regulator composition,in order to induce morphogenesis  相似文献   

12.
The effects of transpiration rate on the vertical gradientsof leaf and stem xylem water potential ( and ) were examinedusing hydroponic sunflower plants. Transpiration was variedby stepwise alterations of environmental conditions. The gradientsof and were relatively small (2.3 and 0.8 x 105 Pa m–1)when transpiration rates approached zero, but increased sharplyto 5.4 and 2.3 x 105 Pa m–1 as transpiration increased.However, the gradients were independent of transpiration ratesabove 0.4 g dm–2 h–1 owing to variability of theplant resistance. The gradients of I were usually less thanhalf those of I. 1 in individual leaves remained constant over a wide range oftranspiration rates (0.4—2.4 g dm–2 h–1) andeach leaf possessed a characteristic plateau value related toits elevation. I responded similarly but was approximately 2.0x 105 Pa higher than I at the same elevation. Identical resultswere obtained regardless of the procedure employed to vary transpiration. The drop in water potential between stem and leaf implies thatthe leaf resistance is appreciable. This was confirmed usingrapidly transpiring excised leaves freely supplied with water.I increased by 2.0–2.5 x 105 Pa following removal of theroot resistance but remained 2 x 105 Pa lower than similar excisedleaves in darkness. Furthermore, I in excised leaves remainedconstant over a wide range of transporting rates, demonstratingthat the leaf resistance is also variable. The results are discussed in relation to previous reports.  相似文献   

13.
Ion contents and concentrations (K+, Na+, Cl, Ca2+, Mg2+,SO2–4, NO3, HPOJ2–4, amino and organic acids)of P. purpurea have been studied in relation to salinity variation.Cells were shown to accumulate large amounts of K+ and Clagainst their respective gradients of electrochemical potentialin all dilute and concentrated seawater media. Active influxof SOJ2–4, NO3, and HPOJ2–4 is also suggested,while Na+ is actively excluded from cells under hyposaline andhypersaline conditions. The relative proportions of individualcomponents of the internal osmotic potential were found to changeaccording to the external salt concentration. KCL forms themajor fraction of j} in concentrated seawater media while K+-aminoacids form the major fraction in dilute seawaters. Other intracellularsolutes comprise less than 15% oftj, in all media. Unidirectional fluxes of K+ and Cl were studied by radioisotopicmeans. Fluxes of K+ and Cl are reduced in hyposalinemedia, as is absolute KCL content per cell. Intracelhilar KCLcontent was also found to be markedly dependent upon externalK+ concentration, rather than water potential. Changes in KC1levels induced by salinity variation occur over a 6 h period.  相似文献   

14.
Hansen, A. P. and Pate, J. S. 1987. Evaluation of the 15N naturalabundance method and xylem sap analysis for assessing N2 fixationof understorey legumes in jarrah (Eucalyptus marginata Donnex Sm.) forest in S.W. Australia.—J. exp. Bot 38: 1446–1458. Nodulated seedlings of Acacia pulchella, A. alata and A. extensawere grown in glasshouse sand culture under a range of levels(0–16 mol m3) of nitrate, supplied as 15NO3, or as unenrichedlaboratory grade nitrate (15N value 5·5%o). Nitrate at8·0 mol m 3 or above was highly inhibitory to growthof all species. Using 15N dilution analysis of the 15N enrichedcultures to measure symbiotic dependency, it was shown that15N values of the parallel unenriched cultures increased innear linear fashion from close to zero in fully symbiotic plantsto values close to that of the supplied NO3 in plants experiencingnitrate levels (4·0 mol m3 or above) inhibiting N2 fixationby over 90%. Xylem sap analyses (0·4 mol m3 NO3 treatments)showed asparagine as the major nitrogenous solute, relativelylittle spill-over of free nitrate, and no evidence of majorshifts in balance of amino compounds with increasing dependenceon nitrate. This essentially invalidated use of the techniqueas a field assay for N2 fixation by the species. 15N values for total N of soil sampled at 64 widely distributedsites in jarrah forest ranged from – 2·15 to +5·4(mean +2·1). Comparable values for soil mineral N (NH+4and NO3) were +0·3 to + 14·2 (mean +5·1).15N values of the total plant N of the legumes and of non-N2-fixingreference species were also highly variable between sites, withlittle evidence of reference plant N accurately reflecting the15N abundance of soil nitrogen, or of visibly well nodulatedlegume components showing consistently lower 15N values thantheir companion reference plants. At one site it was possibleto compare 15N values of first season seedling legumes withpreviously published estimates of their progressive N2 fixationusing C2H2 reduction assays. It was concluded that heterogeneity in 15N discrimination ofsoil within the ecosystem precluded effective use of the 15Nnatural abundance technique for assessing legume N2 fixation. Key words: Acacia spp., 15N natural abundance,, xylem sap analysis,, nitrogen fixation.  相似文献   

15.
Corrigendum     
Light response curves for (•) gross 16O2 evolution, and() CO2 uptake in 210 mmol mol–1 O2 with 900–1000µbar CO2 or () in air by leaves of Hirschfeldia incana.The difference between (•) and () or () was quantitativelyequivalent to the measured 18O2 uptake. The areas under thecurves are labelled to identify regions of assimilatory andnon-assimilatory electron flow redrawn from data of Canvin etal. (1980). It should be noted that the data and the labelling of the figureaxes are correct as printed.  相似文献   

16.
Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m–3 CaCl2 r, P, Y and were20.7±4.6 µm min–1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min–1MPa–1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m–3 KC1 these parametersbecame 12.3±3.5 µm min–1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min–1MPa–1. After 24 h osmotic adjustment in 150 mol m–3mannitol/0.5 mol m–3 CaCl2 r= 19.6±4.2 µmmin–1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min–1 MPa–01, respectively.After 24 h growth in 350 mol m–3 mannitol/0.5 mol m–3CaCl2 r= 13.3±4.1 µm min–1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min–1MPa–1. During osmotic adjustment in 200 mol m–3mannitol/0.5 mol m–3 CaCl2, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min–1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min–1MPa–1. Therefore, Y and are influenced by 10 mol m–3 K+ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur  相似文献   

17.
The effects of two shoot densities (14 and 44 shoots/vine) andtwo crop levels (one and two clusters/shoot) on gas exchangeand water relations of field-grown Sauvignon blanc (Vitis viniferaL.) were studied in a factorial design over 3 years. The two-clustertreatments had 0.14 MPa higher stem water potential (stem),1.4 µmol m–2 s–1 higher assimilation rate(A), 0.04 mol m–2 s–1 higher stomatal conductance(gs) and 0.008 mol m–2 s–1 higher non-stomatal (gm)conductance. The two-cluster treatments had higher gs and transpirationrates than the one-cluster treatments, for similar stem. A quantitativeanalysis suggests that storage capacity cannot account for thesimultaneous increase in gs and stem in the two-cluster treatments.Similar gs-gm responses were found In the one- and two-clustertreatments, regard less of differences between the treatmentsin gs-stem response. Key words: Grapevine, stomatal conductance, assimilation rate, water relations  相似文献   

18.
Uptake of the toxic heavy-metal, thallium, was studied in thecyanobacterium Synechococcus R-2 (PCC 7942) using clinicallyavailable 201Tl +. Thallium was found to distribute across theplasmalemma passively, and so the accumulation ratio of theion ([Tl+]i/[Tl+]o) could be used to calculate the apparentmembrane potential (­i,o) of the cells (ETI+i,o = ­i,o).The permeability of the plasmalemma to TI+ (PTI+ 1 to 5 nms–1)is higher than that of K+. Valinomycin does not increase thepermeability of TI+. Transient changes in the ­i,o of cells,because of electrogenic transport of ions, could be detectedfrom its effects upon the uptake rate of TI+. HCO3 hyperpolarizedSynechococcus cells, whereas NH+4, CH3NH+, and K+ led to depolarization.The use of TI+ as a reporter of ­i,o has some inherent limitations.Tl+ is toxic at very low concentrations (inhibitory effectsare apparent after about 6 h at concentrations as low as 1 mmolm–3). The rate of equilibration is slow (t1/25 to 20 min).Equilibration of TI+ takes about 2 h, which limits its valueas a membrane potential probe. Large amounts of TI+ bind tothe surface of the cells making the method impracticable formeasuring accumulation ratios of less than about 10 (­i,o)values smaller than about –60 mV). Cultures continuouslyexposed to Tl+ (10 mmol m–3) eventually become TI+ resistantby actively extruding TI+ (µTI+i,o= –3±0.2kJ mol–1) and so thallium cannot be used as a ­i,oprobe in such cells. (Received October 28, 1997; Accepted August 31, 1998)  相似文献   

19.
The effects of -hydroxy-2-pyridinemethanesulphonic acid (-HPMS)upon net photosynthesis (Pn, the CO2 compensation point (),post-lower illumination burst of CO2 (PLIB) and post-lower temperatureburst of CO2 (PLTB) in detached rye (Secale cereale L.) leaveswere investigated. At low concentrations ( 0.5 mol m–3),-HPMS initially stimulated Pn and decreased the magnitude ofboth PLIB and PLTB. The decreased at all concentrations of-HPMS (0.05–5.0 mol m–3. The effects of -HPMS onPn and were time-dependent and, after a few minutes, the Pnwas inhibited while values increased considerably. At a higherconcentration (5.0 mol m –3), the transient effects of-HPMS were shorter () or not observed at all (Pn. Both PLIBand PLTB, when expressed in relation to Pn, increased at higherlevels of this compound. Similar data with respect to the effectsof -HPMS on PLIB and PLTB were found for leaves of dandelion(Taraxacum officinale L.). The results suggest that -HPMS may stimulate Pn by inhibitingphotorespiration, as originally suggested by Zelitch (1966),but only at low concentrations and over a short time span. Thedecrease of PLIB and PLTB values at low -HPMS levels is consistentwith these processes being a residual activity of the glycolatepathway. Key words: CO2 compensation point, -hydroxy-2-pyridinemethanesulphonic acid, photorespiration, photosynthesis  相似文献   

20.
The development of taurine uptake into the unicellular greenalga Chlorella fusca 211-8b was characterized as a specificresponse to either nitrate or sulphate limitation. Taurine transportunder nitrogen starvation was stimulated by low pH and showeda biphasic kinetics with Km-values of 1.1 x 10–3 mol dm–3and 1.0 x 10–2 mol dm–3. Uptake was substantiallyinhibited by all - and ß-amino acids tested, whereassulphonate analogues failed to diminish taurine accumulation.Thus, uptake seemed to be mediated by a ‘general aminoacid permease’, unable to discriminate between carboxyland sulphonyl groups. However, Chlorella fusca could not catabolizethis unusual ß-amino acid and mobilize the amino-boundnitrogen for growth. Only a small group of -amino acids supportedthe growth of Chlorella fusca as an efficient nitrogen source. Key words: Taurine uptake, nitrogen starvation, amino acid uptake, Chlorella fusca.  相似文献   

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